dsh-sdk create <source> adds a github (github:owner/repo#ref) or npm (pkg@version)
plugin as a package-manager-native dependency, then mounts the resolved dependency
in cordis.yml through ProjectEditSession. Adds PackageManager.add(spec) and
ProjectEditSession.addExternalPlugin(id, packageName). No giget/pacote. Per-file
100% coverage on the new/changed files.